A Shenzhen branch of US-based retail giant Walmart was accused of selling food beyond its expiry date, of re-using cooking oil in some cases up to a month after it was first used and reselling rice that had been returned by customers.

Local television reported on Thursday that prepared food sold at the Honghu branch of Walmart in Shenzhen was allegedly cooked in oil that had not been replaced for at least two weeks and sometimes for as long as a month.

The supermarket was also accused of selling chicken nuggets and marbled meat beyond its sell-by-date.

There were also allegations that rice returned by customers, which may have been contaminated by bugs, was not discarded but re-used to make fast food.

The video was provided by an employee of the supermarket, and he claimed that their supervisor wanted to "control costs".

The case is under investigation by authorities in Shenzhen.

The branch denied the allegations in the report and said they replaced cooking oil regularly to ensure food safety. They also started internal inspections, according to Shenzhen Television Station.

This is the latest allegation concerning food safety.

Last month, Shanghai Husi Food Company, owned by the US-based OSI Group, was accused by a Shanghai television station of using expired meat and forging production dates to extend shelf time.

The company supplied food to a number of global brands such as McDonald's, KFC, Pizza Hut and Starbucks.

Six senior executives of the company have been arrested by Shanghai police.

The China Food and Drug Administration released a draft document this week inviting the public to give information regarding any food safety concerns.

The draft requires food companies to withdraw substandard food products that present a serious threat to health as soon as they are discovered. Plans for recalls should be submitted to the authorities within 24 hours, it said.